HR: 0800h
AN: C51A-0270    [Abstracts]
TI: Slow Surge of Trapridge Glacier
AU: * Frappe-Seneclauze, T
EM: tfrappe@eos.ubc.ca
AF: Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Clarke, G K
EM: clarke@eos.ubc.ca
AF: Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AB: Trapridge Glacier, Yukon, Canada, is a polythermal, soft-bedded surge-type glacier. As revealed by a 1951 aerial photograph, an important surge occurred in the 1940s, leaving the glacier heavily crevassed and at least 1 km downstream from the 1941 position. It is our conclusion that another surge, albeit far less dramatic, has been taking place over the last three decades and is now terminated. To quantify the changes in ice geometry, ground survey measurements were coupled with aerial photogrammetry to yield digital elevation models of the glacier from 1951 to present. For 1951, 1970, 1972, 1977 and 1981, years for which ground data are scarce or unavailable, DEMs were generated from stereographic analysis of aerial photographs. For the subsequent years, DEMs are obtained from ground survey data using our implementation of a Bayesian Kriging algorithm. For each year, the topography of the previous year is used as a background model and updated by the available survey data. This chain is initiated by the 1981 DEM obtained from aerial photogrammetry. Using exposed sections of the bed from the 1981 DEM and radar data, a map of the bed topography is obtained. Changes in the flow patterns are also investigated using an extended but variable array of flow markers. The results of this work indicate that the period from the previous surge to the present was characterized by two processes: 1) the deglaciation of the 1940s surge `receiving area' and 2) the slow advance of a mass wave from the upper reaches of the glacier. While it was previously believed that this mass reorganization was to precede a fast surge, it is now obvious that such a surge is not to happen. Ice velocity peaked at nearly 40 m/yr in the mid 1980s, fluctuated for the next 15 years and then dropped ca 2000 to reach ~10 m/yr in 2005. The bulge that formed in the 1980s at the transition between warm- and cold-based ice continued to propagate beyond the limits of the 1981 glacier. The glacier snout is currently ~200 m downstream from the 1981 terminus and not advancing. Together the DEMs and bed topography map enable us to characterize changes in the distribution and volume of ice, hydrological potential, and basal stress that accompanied the slow surge.
DE: 0720 Glaciers
DE: 0762 Mass balance (1218, 1223)
DE: 0774 Dynamics
DE: 0798 Modeling
DE: 1827 Glaciology (0736, 0776, 1863)
SC: Cryosphere [C]
MN: Fall Meeting 2005